Re: [PATCH 1/3] memory: extern memory_block_size_bytes and set_memory_block_size_order

[Gregory Price]

On Tue, Oct 08, 2024 at 05:02:33PM +0200, David Hildenbrand wrote:
> On 08.10.24 16:51, Gregory Price wrote:
> > > > +int __weak set_memory_block_size_order(unsigned int order)
> > > > +{
> > > > +	return -ENODEV;
> > > > +}
> > > > +EXPORT_SYMBOL_GPL(set_memory_block_size_order);
> > > 
> > > I can understand what you are trying to achieve, but letting arbitrary
> > > modules mess with this sounds like a bad idea.
> > > 
> > 
> > I suppose the alternative is trying to scan the CEDT from inside each
> > machine, rather than the ACPI driver?  Seems less maintainable.
> > 
> > I don't entirely disagree with your comment.  I hummed and hawwed over
> > externing this - hence the warning in the x86 machine.
> > 
> > Open to better answers.
> 
> Maybe an interface to add more restrictions on the maximum size might be
> better (instead of setting the size/order, you would impose another upper
> limit).

That is effectively what set_memory_block_size_order is, though.  Once
blocks are exposed to the allocators, its no longer safe to change the
size (in part because it was built assuming it wouldn't change, but I
imagine there are other dragons waiting in the shadows to bite me).

So this would basically amount to a lock-bit being set in the architecture,
beyond which block size can no longer be changed and a big ol' splat
can be generated that says "NO TOUCH".

> Just imagine having various users of such an interface ..

I don't wanna D:

> 
> -- 
> Cheers,
> 
> David / dhildenb
>